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Test Code IOCA Calcium, Ionized, Serum

Specimen Type

Preferred: Serum

Acceptable: Plasma


Preferred: Serum Red Top tube or Gold SST

Acceptable: Lithium Heparin (Mint Green or Dark Green)


*NOTE: Heparinized plasma may give slightly lower results due to binding by the heparin.


Preferred Volume

5 mL

Offsite Collection Instructions

1. The tube for the ionized calcium MUST REMAIN CAPPED to prevent exposure to air.

2. Serum and plasma tubes should be centrifuged and aliquoted within 2 hours of collection.

3. Aliquoted samples should be refrigerated at 2-8°C prior and during transportation.

4. If above criteria are not met, specimen will be rejected.

UCMC Collection Instructions

1. The tube for the ionized calcium MUST REMAIN CAPPED to prevent exposure to air.

2. Samples need to be received in the lab within 2 hours of collection at room temperature.

3. Greater than 2 hours must be refrigerated at 2-8°C.

4. If the specimen cannot be sent to the lab within 6 hours of collection, it must be spun, aliquoted and refrigerated at 2-8°C.

5. All unspun specimens greater than 6 hours will be rejected.  

6. If above criteria are not met, specimen will be rejected.



Turnaround Time

4 hours

STAT Availability


Test Usage

Useful in assessing calcium states during any procedure requiring rapid transfusion of whole blood in neonates and in critically ill patients.
Second-order test in the evaluation of patients with abnormal calcium values.

Test Methodology

Ion-specific electrode

Additional Information

Ionized calcium values vary inversely with pH, approximately 0.2 mg/dL per 0.1 pH unit change.

CPT Code


STAT Turnaround Time

1 hour

Reference Range

4.60 – 5.40 mg/dL

Critical Results


Test Limitations

Gross hemolysis may falsely elevates results.
Patients receiving citrate-containing blood or blood fractions may have increased total serum calcium, despite decreased ionized calcium.
Low protein stores may falsely lower results.

Minimum Volume

2 mL

Coverage Information

CMS local coverage decision for “Ionized Calcium” retired effective 3/14/12. For more details click this link:



Test Includes

Quantitative determination of ionized calcium in plasma

Fee Code